The present invention relates to an information processor operating with a battery such as a portable personal computer, word processor, terminal device for work station, and computer with hand writing pen input device and more particularly to an information processor having a resume function which is a characteristic of an information processor operating with a battery and is improved.
Conventionally, suspending processing for stopping a CPU (central processing unit) when a computer is not to be used temporarily and resuming the CPU to the state before stopping the CPU when reusing the CPU from the suspended state are performed as resume function management. If a computer which has not the aforementioned suspend function and resume function is left as it is when it is not to be used temporarily, the power consumption during operation is required as it is and an increase in power consumption results. When all softwares end, and power is turned off, and all the softwares are restarted so as to reuse them, the power consumption is increased due to these processings. By adding and using the suspend function and resume function, the power consumption can be reduced.
The following methods are conventionally known as such a suspend method and resume method.
(i) A method for stopping only the CPU clock (Japanese Patent Application Laid-Open No. 58-205226)
(ii) A method for reading the CPU state into the outside of the CPU, transferring it to a memory, and turning the CPU off (Japanese Patent Application Laid-Open No. 3-27419)
(iii) A method for recording contents of the CPU and memory in a non-volatile memory device such as a hard disk and turning the CPU and memory off (Japanese Patent Application Laid-Open No. 56-108119, Japanese Patent Application Laid-Open No. 57-94821)
The following two points are most important factors in the above three methods. Namely, they are the power consumption required in the suspended state when the CPU is stopped (hereinafter called power consumption in the suspended state) and the time and power consumption required for the transfer transaction from the normal operation state to the suspended state when the CPU is stopped (hereinafter called suspend transaction time and suspend transaction power consumption). When the aforementioned three methods are discriminated from the above two viewpoints and lined up in the ascending order of magnitude of power consumption in the suspended state, the order is (iii), (ii), and (i). When the methods are lined up in the ascending order of magnitude of suspend transaction time and suspend transaction power consumption, the order is (i), (ii), and (iii).
Such suspension of processing is often used in a miniature information processor operating with a battery recently as an effective means for reducing power consumption.
The method (iii) mentioned above is excellent in the power consumption reduction effect and the power consumption in the suspended state may be reduced to 0. Therefore, data erasure and file system destruction due to insufficient power of a battery will not be caused. However, the method (iii) requires the suspend transaction time and suspend transaction power consumption in proportion to the memory amount to be transferred, so that as the memory capacity of an information processor is increased, the suspend transaction time is increased and the suspend transaction power consumption is also increased. Therefore, firstly when the suspend transaction time is increased, the suspend function is hard to use and secondly when the suspend function and resume function are performed for a short time, not only the power consumption reduction effect is lost but also the power consumption is increased.
Therefore, a method for shortening the suspend transaction time using the methods (i) and (ii) mentioned above and reducing the suspend transaction power consumption may be considered. However, the methods (i) and (ii) cannot reduce the power consumption in the suspended state to 0. Therefore, there is a possibility that the power of the battery is exhausted during suspension of drive of the battery in the worst case. If this occurs, the data is erased and furthermore the file system may be destroyed.
As mentioned above, according to the conventional methods, even when the method (iii) is used, the suspend transaction time is increased as the capacity of a memory is increased and when the CPU is suspended for a short time, the power consumption is also increased. On the other hand, the methods (i) and (ii) cannot take action when the power of the battery becomes insufficient during suspended state.